Secret lover Mellon mourns for Issie Blow

But there was one mourner among the A-list throng who harboured a very private heartache.

Clothes designer and oil heir Matthew Mellon, who was seated in the front row at the service with Isabella's sister Julia Delves Broughton, had a clandestine four-month affair with the Tatler fashion editor, who killed herself in May, at the age of 48, by drinking weedkiller.

The relationship, a closely guarded secret among Issie's friends, started in 2004 after she had separated from her husband, gallery owner Detmar Blow, and Matthew had split from Jimmy Choo boss Tamara Mellon.

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Affair: Isabella and Matthew Mellon

"They were both single and fell passionately in love," a friend said.

"Issie was at a low point and Matthew was there to offer support. She called him Mellon Juice and adored him."

"Matthew whisked Isabella off to the South of France, where he chartered a yacht and they had a blissful time.

"On the flight home, Issie said she had to see her husband.

"Matthew encouraged her to do so, and although their affair ended, he stood by her to the end."

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Before their separation: Matthew with Tamara Mellon

Matthew, 43, visited Isabella every day for six months after she tried to kill herself by leaping off a bridge in West London in 2005.

The friend added: "Issie would often say she just wanted to be taken care of and Matthew was in a position to do that."

Far from being strained, relations between Isabella's two great loves are cordial and Matthew was invited to lunch with the family after last week's service.