Russell Brand and Jemima Khan, who have been dating since last summer, have sparked engagement rumours after the beauty was spotted wearing a diamond ring in London and another day in a restaurant.A source told the Mirror that the sparkler looked like an engagement ring and was very pretty and classy.The insider asserted that 40-year-old Khan looked very happy.Although, the 38-year-old comedian, who was earlier married to signer Katy Perry, has openly confessed to being in love with the mum-of-two, the pair hasn't officially announced anything yet."It looked like an engagement ring. It was very pretty and classy. She looked very happy," the source said.Jemina has two sons with former cricketer Imran Khan. She also dated actor Hugh Grant.