Jennifer Lopez donned a wetsuit to complete her first triathlon just before turning heads in a stunning gown at her husband Marc Anthony's surprise birthday party in New York.

The 39-year-old singer and actress - who gave birth to twins just seven months ago  - played the proud wife at the bash after taking part in the three-part race.

Transformation: Jennifer Lopez at husband Marc's birthday party on Saturday night and in a wetsuit during the triathlon on Sunday

The couple celebrate Marc's birthday at the Bowery hotel in New York

She reached the finishing line after an impressive two hours, 23 minutes and 28 seconds, despite having an ankle injury.

During the event Lopez swam, ran and biked as she worked up a sweat to raise more than £70,000 for the Children's Hospital of Los Angeles.

The star was cheered on by husband Marc Anthony, who even managed to sneak a kiss off her between the swimming and biking part of the event.

Quick change: Lopez arrived at the party in a white gown but left with a totally different dress and hairstyle

Action woman: Lopez sharing an embrace with Marc and during the race 

She was also joined by fellow actor Matthew McConaughey who she starred alongside with in the 2001 romantic comedy The Wedding Planner.

Not to be outdone, McConaughey finished the event after one hour, 30 minutes and 44.7 seconds.

But Lopez was ecstatic as she crossed the finishing line.

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Ecstatic: Jennifer Lopez reaches the finishing line after two hours, 23 minutes

Lopez was inspired to take part in the triathlon when she was eight months pregnant with twins Max and Emme.

She told ABC's Good Morning America last month: 'I was beached like a whale. I was watching TV, and I saw a triathlon and I said, "You know what? I think I could do that, that would be great for me to do. Maybe I'll do it this year."'

Lopez gets a kiss of support from her husband Marc

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On her bike: The star completes the cycling race

In the VIP area, Lopez met up with McConaughey. They both greeted each other with a hug following their efforts at event, held at Zuma Beach.

Lopez was accompanied along the way by her trainer Gunnar Peterson who was not officially taking part.

McConaughey's girlfriend Camila Alves and their newborn son Levi were there to show their support. Actor Jon Cryer also took park in the triathlon.

In total the event raised nearly £530,000.

Wearing her sporty attire today, Lopez cut a very different image to last week when she was pictured in a stunning white dress with Victoria Beckham at New York Fashion Week.

xFitness buff: McConaughey finished the event after one hour, 30 minutes and 44.7 seconds