Adam Golstein and Nicole RichieNicole Richie and Adam GoldsteinIt's a well-documented fact... the course of celebrity love never runs smooth.

And no-one proves it more than Nicole Richie.

She and boyfriend Adam Goldstein split in December, got it back on again... and now Nicole's dad has revealed a surprising new twist.

Legendary singer Lionel Richie says Nicole and Adam are not just back together - they're planning a trip down the aisle.

He broke the good news to the Daily Mirror before he took to the stage at the Prince's Trust concert in London on the weekend.

Lionel, who's Nicole's adoptive father, said: "I told her: 'Honey, you do what you want and just send me the bill.'

"I'm really happy that it's working out for her," said the 56-year-old former Commodores star.

Nic and Adam, who first got together in 2003, are rumoured to be planning a July wedding.

But a note of caution: Lionel may want to save receipts for everything he splashes out on.

US Star magazine has just reported that the pair have split up again... We're officially confused.

Even Lionel hinted that he still has concerns over Nicole, who recently admitted to Vanity Fair magazine that she's "too thin".

Lionel said: "She really needs a vacation. She's a great girl and she's really been through a lot."