Pippa Middleton enjoyed a low-key outing in London on Monday afternoon as she embarked on a stroll with her four month old daughter Grace.The 37-year-old, who is the younger sister of the Duchess of Cambridge, welcomed her little bundle of joy four months ago in March with husband James Matthews, with who she also shares three year old son Arthur. And Pippa looked happy and relaxed as she pushed a stroller while basking in the evening sunshine along the streets of Chelsea.